In a parallax barrier type 3D display device, pixels of a display panel alternately display a left eye image and a right eye image by columns, and by arranging a parallax barrier parallel to the display panel in front of the display panel or between the display panel and a backlight source and using a light-shielding effect of a grating sheet of the parallax barrier, a left eye of a viewer and a right eye respectively see the left eye image and the right eye image displayed in the pixels of the display panel, and thus, the stereoscopy can be achieved without wearing a stereoscopic glasses, wherein, the grating sheet is a black stripe having the light-shielding effect in the parallax barrier. In addition, isolation pixels can be arranged between the pixels displaying the left eye image and the pixels displaying the right eye image to prevent dizzy phenomenon.
The theoretical value Ctheory of a grating pitch is a parameter value theoretically calculated according to the structure model of the parallax barrier, and the Ctheory has different theoretical derivation formulas depending on uses of the parallax barrier, for example, the theoretical derivation formula of a two-viewpoint rear parallax barrier 3D display device is different from that of a two-viewpoint front parallax barrier 3D display device. FIG. 1 is a principle view of the light path of a current two-viewpoint rear parallax barrier 3D display device, and the 3D display device comprises a display panel 100 and a parallax barrier 200 parallel to it. For the parallax barrier type 3D display device, in order to achieve the stereoscopic display, it is necessary to shield a part of light from a light source by grating sheets 210 of the parallax barrier after the parallax barrier is arranged, so that the left eye of a viewer can only see the pixels 110 displaying the left eye image and the right eye of the viewer can only see the pixels 120 displaying the right eye image. In other words, in order to achieve the stereoscopic display, the parallax barrier should be aligned with the display panel accurately, so that the left eye of the viewer can only see the pixels of the left eye image and the right eye of the viewer can only see the pixels of the right eye image; on the contrary, if the parallax barrier is not aligned with the display panel accurately, the left eye of the viewer cannot see the pixels of the left eye image and the right eye of the viewer cannot see the pixels of the right eye image, thus the stereoscopic display cannot be achieved.
Exemplarily, in order to achieve the accurate alignment between the parallax barrier and the display panel, parameter design formulas of the parallax barrier of the two-viewpoint rear parallax barrier 3D display device is illustrated as follow: h=p×s÷(l−p), and Ctheory=2×p×l÷(l−p), wherein, s is the best viewing distance, l is a distance between two eyes, and h is a placing height of the parallax barrier, and the placing height of the parallax barrier is a distance between the parallax barrier and a surface facing the parallax barrier of the display panel, p is a pixel length of the display panel in an arrangement direction of the grating sheets of the parallax barrier, Ctheory is a theoretical value of a grating pitch which is a pitch between two adjacent grating sheets. Thus, by using the parameter design formulas of the parallax barrier, the theoretical value of the grating pitch Ctheory when the parallax barrier is accurately aligned with the display panel can be calculated.
From the parameter design formulas of the parallax barrier, the theoretical value of the grating pitch Ctheory is relevant to the length pixel p of the display panel and is slightly larger than twice of the length pixel p. Under the influence of a practical fabrication accuracy, an actual value of a grating pitch Cactual is different in some way from the theoretical value of the grating pitch Ctheory. For example, the practical fabrication process is usually designed by taking 0.00025 mm or 0.0005 mm as a minimum accuracy. Considering the fabrication accuracy, the actual value of the grating pitch of a conventional parallax barrier only satisfies a relationship of Cactual=2p+practical fabrication accuracy of a parallax barrier, then
                                          C            actual                    -                      C            theory                          =                ⁢                              2            ⁢            p                    +                      practical            ⁢                                                  ⁢            fabrication            ⁢                                                  ⁢            accuracy            ⁢                                                  ⁢            of            ⁢                                                  ⁢            a                                                          ⁢                              parallax            ⁢                                                  ⁢            barrier                    -                      2            ×            p            ×                          l              ÷                              (                                  l                  -                  p                                )                                                                                      =                    ⁢                      practical            ⁢                                                  ⁢            fabrication            ⁢                                                  ⁢            accuracy            ⁢                                                  ⁢            of            ⁢                                                  ⁢            a                          ⁢                                                                  ⁢                              parallax            ⁢                                                  ⁢            barrier                    ⁢                                          -                                          ⁢                      2            ⁢            p            ×                          (                                                l                  ÷                                      (                                          l                      -                      p                                        )                                                  -                1                            )                                                              =                ⁢                              practical            ⁢                                                  ⁢            fabrication            ⁢                                                  ⁢            accuracy            ⁢                                                  ⁢            of            ⁢                                                  ⁢            a            ⁢                                                  ⁢            parallax            ⁢                                                  ⁢            barrier                    -                                                ⁢                  2          ×          p          ×                      p            ÷                                          (                                  l                  -                  p                                )                            .                                          
It can be known from the above that an error between Cactual and Ctheory is relevant to the fabrication accuracy of the parallax barrier, p and l. There is such error between each actual value of the grating pitch Cactual and the theoretical value Ctheory of the grating pitch, and the error is a positive number or a negative number, Y is defined to be a alignment error of the parallax barrier, then Y=practical fabrication accuracy of a parallax barrier−2×p×p÷(l−p), and the more the number of the grating sheets of the parallax barrier is, the larger the alignment error Y at two edges of the parallax barrier is.
For example, for a 4-inch parallax barrier type 3D display device, the pixel length p of the display panel in a length direction of the display panel, i.e., the arrangement direction of the grating sheets of the parallax barrier, is 0.111 mm, the best viewing distance s is 300 mm, the distance l between two eyes is 65 mm, according to the formulas of h=p×s÷(l−p) and Ctheory=2×p×l÷(l−p), and taking the practical fabrication accuracy of 0.0005 mm as an example, it can be obtained that the alignment error Y≈0.00012 mm.
As shown in FIG. 2, the grating pitches of the conventional parallax barrier are the same. Suppose that there are 400 grating sheets included in the current parallax barrier in the length direction of the display panel, and the current parallax barrier is usually aligned with the display panel at a central position of a horizontal direction, an alignment error between a pixel of the display panel at the central position of the horizontal direction and the corresponding grating sheets is 0.00012 mm, while an alignment error between the pixels at two edges of the central position of the horizontal direction and the corresponding grating sheets will be larger, for example, the alignment error between the nth grating sheet and the corresponding pixel is n×0.00012 mm, while the alignment error between the pixels at the outermost edge and the corresponding grating sheets is 200×0.00012 mm=0.024 mm. A proportion of the alignment error in one pixel region of the display panel is 0.024÷0.111×100%=22%, thus a serious crosstalk can be caused, and a viewing angle and a brightness uniformity of stereoscopic display are reduced, and a viewing effect of stereoscopic display is seriously affected.